http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50251
--- Comment #16 from vries at gcc dot gnu.org 2011-09-02 22:47:42 UTC ---
Started testing patch from comment 9, augmented with comments:
...
Index: explow.c
===================================================================
--- explow.c (revision 178145)
+++ explow.c (working copy)
@@ -1062,6 +1062,20 @@ emit_stack_restore (enum save_level save
/* The default is that we use a move insn. */
rtx (*fcn) (rtx, rtx) = gen_move_insn;
+ /* If stack_realign_drap, the x86 backend emits a prologue that aligns both
+ STACK_POINTER and HARD_FRAME_POINTER.
+ If stack_realign_fp, the x86 backend emits a prologue that aligns only
+ STACK_POINTER. This renders the HARD_FRAME_POINTER unusable for accessing
+ aligned variables, which is reflected in ix86_can_eliminate.
+ We normally still have the realigned STACK_POINTER that we can use.
+ But if there is a stack restore still present at reload, it can trigger
+ mark_not_eliminable for the STACK_POINTER, leaving no way to eliminate
+ FRAME_POINTER into a hard reg.
+ To prevent this situation, we force need_drap if we emit a stack
+ restore. */
+ if (SUPPORTS_STACK_ALIGNMENT)
+ crtl->need_drap = true;
+
/* See if this machine has anything special to do for this kind of save. */
switch (save_level)
{
...
